Generally, transfer presses include a two-dimensional or three-dimensional transfer feeder and such transfer feeders have clamp units and a feeding unit. In the case of three-dimensional transfer feeders, lift units are further provided. More specifically, it is usually the case that a plurality of clamp units are mounted within the main body of the transfer press and that where a three-dimensional feeder is employed, a plurality of lift units are also mounted within the main body of the transfer press. The feeding unit is generally projectively mounted in the downstream side of the press body when viewed in a workpiece feeding direction.
FIGS. 7 and 8 are a side view showing a feeding stroke end (feeding end) condition of a prior art feeding unit and a side view showing a feed bar split condition of the feeding unit, respectively. This prior art feeding unit for a transfer press will be explained with reference to FIGS. 7, 8, while referring to FIG. 1 as a basic construction for a feeding unit for a transfer press, FIG. 1 showing a general side view of a transfer press according to the present invention.
In FIGS. 7 and 8, a feeding unit 105 (corresponding to a feeding unit 5 in FIG. 1) extends from the most upstream area to the most downstream area of the press machine and retains workpieces with fingers attached to two feed bars 4 that are opposed to each other in the front and rear direction of the press (i.e., the direction perpendicular to the workpiece feeding direction shown in the drawings). By moving the feed bars 4 two-dimensionally or three-dimensionally, the workpieces are successively conveyed to the next work station or idle station. A pair of uprights 3 (3′) are provided in the most upstream and downstream areas and between every two slides 2 of the transfer press 1, so as to stand up on the bed. Each slide 2 moves up and down along slide guides (not shown) provided in the uprights 3 (3′).
The feeding unit 105 has (i) a feed driving means 110 that includes servo motors 111 serving as a driving source for the feeding unit and pinions 112 rotatively driven by the servo motors 111; (ii) feed racks 120 that mesh with the pinions 112 and freely reciprocate in the workpiece feeding direction; (iii) feed carriers 130 integrally attached to the undersides of the feed racks 120; (iv) cylindrical coupling bars 131 that are disposed at the undersides of the feed carriers 130 so as to be movable in a clamping direction (i.e., the front and rear direction of the press) and have a central axis extending in a vertical direction; (v) a feed box body 140 for supporting these members; (vi) feed bars 4 each having one end coupled to the coupling bar 131 such that the feed bar 4 is movable in a lifting direction (i.e., vertical direction) and each supported by a clamp/lift unit 6 disposed between every right and left pair of uprights 3 (3′) so as to move in the feeding direction; and (vii) fingers 7 detachably attached to the feed bars 4 for retaining the workpieces.
For off-line set-up of the fingers at the time of die replacement, each feed bar 4 has a detachable split section and a part of the feed bars 4 is placed on a moving bolster 8 so as to be carried out of the press together with the dies.
The feed box body 140 is cantilevered with one end being attached to the downstream outer side faces of the uprights 3 in order to avoid interference with a carry-out device disposed at the downstream area of the press and to achieve improved workability in carry-out of a workpiece.
In the prior art, the feed driving means 110 is, however, located in the vicinity of the leading end of the cantilevered feed box body 140, being a certain distance (the distance L2 in FIG. 7) away from the uprights 3 as shown in FIGS. 7, 8. The feed driving means 110 is a heavy high-capacitance member composed of large-sized, extremely heavy servo motors and others and therefore the installation of the feed driving means 110 at a distance from the uprights 3 entails the following problems.
During forming of a workpiece, violent vibration occurs in the press body, so that the feed box body 140 receives forced vibration through its fixed end and therefore the feed bars 4, which are coupled to the feed box body 140 through the feed carriers 130, vibrate in turn. This causes a feeding error (conveying error), bringing the press machine to a sudden stop with the result that the machine utilization rate and productivity of the press machine drop. In some cases, the vibration of the feed box body 140 is reversely transmitted to the press body, which is a cause of a decrease in the accuracy of the workpiece forming operation. Further, the susceptibility to a workpiece feeding error and a decrease in the accuracy of the workpiece forming operation puts restrictions on workpiece feeding speed (i.e., the conveying speed of the feed bars) so that the production capacity of the press cannot be increased.
In addition, since the location of the feed box body 140 with respect to the feeding direction of the feed driving means 110 is in the vicinity of the stroke end of the feed carriers 130, the stroke end being located on the side opposite to the press body, when the feed carriers 130 are moved in the direction away from the press body, the end of each feed rack 120 projects from the feed box body 140. To prevent the feed racks 120 from being exposed, a rack cover is disposed at a side face of the feed box body 140. Since the rack cover for covering the projecting portions of the feed racks 120 is located at a level substantially equal to human head height, workability in taking-out of a workpiece by hand and in the maintenance of the parts in this area is impaired.
In addition, the entire length (length L02 in FIG. 7) of the feeding unit 105 in the feeding direction and the size of the feeding unit 105 are significant. This not only increases the manufacturing cost of the feeding unit but also the entire length of the press, and as a result, the installation area of the press and the mechanical equipment cost increase.
As shown in FIGS. 7 and 8, the conventional feeding unit 105 has a stopper 161 at the feeding stroke end in the downstream area of the feeding unit 105, for preventing the driving motors from running out of control. Since this stopper 161 needs to be made of a large-sized cushioning material (e.g., rubber) in order to adsorb the kinetic energy of the movable part of the feeding unit 105 during run-away of the feeding unit and to mitigate its shocks, the stopper 161 is considerably thick in the feeding direction. The contact face of the stopper 161 is a certain distance away from the feeding end of the feed carriers 130 in the direction opposite to the press body, the distance corresponding to a bar splitting stroke. The stopper 161 is fixedly (permanently) attached to the underside of the feed box body 140 through a bracket 162. For keeping the installation space for the stopper 161, the entire length (length L02 in FIG. 7) of the feeding unit 105 in the feeding direction becomes long and the feeding unit 105 becomes large in size. Therefore, not only the manufacturing cost of the feeding unit 105 but also the entire length of the press machine is increased, entailing an increase in the installation area of the press machine and the mechanical equipment cost.
The present invention has been made in consideration of the shortcomings described above and a primary object of the invention is therefore to provide a feeding unit for a transfer press, which is small in size so that the entire length of the press machine can be reduced, leading to reduced equipment cost.